全文获取类型
收费全文 | 3076篇 |
免费 | 155篇 |
国内免费 | 302篇 |
专业分类
林业 | 242篇 |
农学 | 127篇 |
基础科学 | 132篇 |
427篇 | |
综合类 | 1012篇 |
农作物 | 137篇 |
水产渔业 | 198篇 |
畜牧兽医 | 939篇 |
园艺 | 171篇 |
植物保护 | 148篇 |
出版年
2024年 | 15篇 |
2023年 | 59篇 |
2022年 | 87篇 |
2021年 | 145篇 |
2020年 | 107篇 |
2019年 | 128篇 |
2018年 | 87篇 |
2017年 | 122篇 |
2016年 | 132篇 |
2015年 | 122篇 |
2014年 | 164篇 |
2013年 | 193篇 |
2012年 | 241篇 |
2011年 | 232篇 |
2010年 | 166篇 |
2009年 | 181篇 |
2008年 | 148篇 |
2007年 | 166篇 |
2006年 | 150篇 |
2005年 | 117篇 |
2004年 | 90篇 |
2003年 | 90篇 |
2002年 | 87篇 |
2001年 | 64篇 |
2000年 | 56篇 |
1999年 | 46篇 |
1998年 | 28篇 |
1997年 | 44篇 |
1996年 | 29篇 |
1995年 | 37篇 |
1994年 | 27篇 |
1993年 | 33篇 |
1992年 | 21篇 |
1991年 | 31篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1974年 | 1篇 |
1956年 | 3篇 |
排序方式: 共有3533条查询结果,搜索用时 15 毫秒
951.
Soto R Rubio I Galina CS Castillo E Rojas S 《Tropical animal health and production》2001,33(3):253-264
This experiment studied the combined effect of pre- and post-calving feed supplementation on the productive and reproductive performance of primiparous Brahman cows. The animals were 4 years old (420 kg live weight) and pregnant, and grazed rotationally on Stargrass (Cynodon nlemfuensis) pastures. Supplementation was given before and after (T1, n = 15), only before (T2, n = 15) or only after (T3, n = 16) calving, and there was an unsupplemented control (T4, n = 16). The supplement (1.5 kg/animal per day, 13.4 MJ digestible energy/kg dry matter and 20% crude protein) was given for 45 days before and/or after calving. Changes in body weight and body condition score and the productive behaviour of the calves were similar (p>0.05) among treatments. The concentration of urea in the plasma was low in the control group (T4) before and after calving. The animals in all the groups had a poor reproductive performance. The percentage of cows in oestrus was higher (p<0.05) in T1 (73.3%) than in T3 (37.5%). The interval from calving to conception (148.7±53.7 days) and the pregnancy rate (48.5%) were similar (p>0.05) among the treatments. The level of supplementation offered before and/or after calving did not improve the pregnancy rate. 相似文献
952.
Veterinary Research Communications - 相似文献
953.
Liberati TA Sansone SR Feuston MH 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2004,33(2):68-73
BACKGROUND: The Wistar Hannover rat has been considered as an alternative animal model to the Sprague-Dawley rat in the safety evaluation of candidate pharmaceuticals for potential reproductive and developmental toxicity. Hematology and clinical chemistry results may provide useful evidence of maternal toxicity in the absence of fetal effects. OBJECTIVE: The purpose of this study was to evaluate differences in routine laboratory values between nonmated and pregnant (near-term)Wistar Hannover rats during a control developmental study. METHODS: One hundred fifty pregnant female Wistar Hannover rats (Tac:Glx:WlfBR) were dosed orally once per day with distilled water from gestation days (GDs) 6 through 17. An additional 150 nonmated (nonpregnant) females used as age-matched controls were dosed from study days (SDs) 7 through 18. Blood samples were collected on GD 18 or 19 (SD 19 or 20) for routine hematology and plasma clinical chemistry tests. Reference intervals were established for pregnant and nonmated animals. RESULTS: On GD 18/19, pregnant rats had a lower RBC count, hemoglobin concentration, and HCT, and higher MCH, MCHC, reticulocyte percentage, and platelet, WBC, absolute reticulocyte, segmented neutrophil, lymphocyte, and monocyte counts compared with nonmated rats. Pregnant rats had lower albumin, glucose, urea, and chloride concentrations, lower creatine kinase and alkaline phosphatase activities, higher total bilirubin, cholesterol, triglyceride, calcium, phosphorus, and globulin concentrations, and higher ALT activity than nonmated rats. Serum triglyceride concentration was approximately fourfold higher in pregnant rats compared with nonmated controls. CONCLUSION: Differences in hematology and chemistry values in pregnant Wistar Hannover rats are similar to those in Sprague-Dawley rats and support use of the Wistar Hannover rat as an animal model in the assessment of maternal toxicity. Differences in laboratory values of pregnant rats should be considered when interpreting data following exposure to candidate pharmaceuticals. 相似文献
954.
The impact of anatomic location on trichogram analysis of the hair cycle phases was evaluated in 15 clinically normal dogs. The purposes of this study were to determine if the number of hairs in anagen and telogen vary among anatomic sites within a dog and to see whether there is an optimal region to sample hairs for canine trichogram evaluation of the hair cycle phases. In each dog eight sites were sampled. Four (26.7%) of the 15 dogs had no significant differences in the number of hairs in anagen and telogen among the eight body sites examined. Nine (81.8%) of the remaining 11 dogs had only one site that revealed significant differences in the number of hairs in anagen or telogen. In seven (77.8%) of these dogs only the anagen differed significantly, and in two (22.2%) dogs both phases differed significantly. Two (18.2%) dogs revealed two sites with significant differences in the number of hairs in anagen. The number of hairs in anagen and telogen in the shoulder area did not vary significantly in any of the dogs. This observation, coupled with the ease of sampling at this site, indicates that the shoulder is the site of choice when studying variations in ratios of hair cycle phases using unit area trichogram. Our results also suggest that numbers of telogen and anagen hairs from body regions with different hair shaft lengths do not vary significantly, and the occasional inconsistent results noted at some body sites might be due to sample collection technique. 相似文献
955.
AIM: To observe the inhibitory effects of polypeptide from Buthus martensii venom (PBMV) on human tumor cell lines and the influence of PBMV on cell cycle migration, expression of tumor-suppressor gene p53 and the membrane potential of CNE-2Z cells. METHODS: MTT colorimetric method, the colony formation and mitosis index, flow cytometry assay and intracellular recording with glass microelectrodes were used. RESULTS: PBMV had obvious cytotoxicity on several tumor cell lines. The cells grow was inhibited by PBMV, colony formation rate and mitotic index of tumor cells were reduced and the number of polykaryocyte was decreased. CNE-2Z cells in S phase were reduced evidently after they were treated with PBMV (P<0.01). After CNE-2Z cells were incubated with PBMV, P53 protein expression in the cells decreased obviously. Differences were very distinct (P<0.01). The negative potential of cell membrane reduced evidently and cell membrane was in depolarization state. CONCLUSION: PBMV probably possesses the effects of the "membrane toxin". By decreasing the membrane potential, the growth and proliferation of tumor cells were interfered by PBMV. 相似文献
956.
外源性环核苷酸对AA肉鸡脂肪和蛋白质代谢的影响 总被引:3,自引:0,他引:3
选用初生健康AA肉鸡 2 4 0只 ,随机分为 2组 ,每组 12 0只 ,每组内设 3个重复 :I组为试验组 ,每隔 4d皮下注射标准环核苷酸组合剂 ,剂量为每只鸡 0 1mL ;Ⅱ组为对照组 ,注射等量的生理盐水 ,共计 4 9d。研究结果表明 ,试验组鸡肝脏组织中总RNA、mRNA分别比对照组提高2 9 84 %和 2 6 0 3%。经单因子方差分析 ,组间均存在着显著差异 (P <0 0 1) ,血浆中cAMP和cGMP的浓度显著高于对照组 (P <0 0 1) ;血清中生长激素浓度升高 37 70 % ,球蛋白浓度提高了 34 0 9% ,甘油三酯浓度显著高于对照组 (P <0 0 1) ,尤其GOT、GPT等酶活性均有显著提高 (P <0 0 1)。 相似文献
957.
958.
The interactions between the collembolan Mesaphorura krausbaueri and four soilborne plant pathogenic fungi all living in the same layer of agricultural soil were studied under laboratory conditions. Mycelia of Gaeumannomyces graminis var. tritici, Fusarium culmorum and Rhizoctonia cerealis were palatable to Collembola and were a food source adequate for reproduction. Hyphae of Bipolaris sorokiniana were toxic and repellent for M. krausbaueri, but its conidia were eaten and proved to be a sufficient diet for reproduction. The four fungi fed had a different impact on the life processes of M. krausbaueri. Depending on the species of fungus, the animals produced significantly different numbers of eggs and had different life spans. In particular, animals fed with G. graminis var. tritici showed early maturation, early burst in egg production, early loss of fertility and early death. The different nutritional values of the four fungi pathogen for cereals might have a different influence on the life strategy of Collembola in the field. Thus, since these fungi usually coexist in agricultural soils, though in different percentages, this influence might also affect the capacity of different fungi to attack the plant and thus modulate the appearance of disease. 相似文献
959.
Amusium laurenti is a functional hermaphroditewith well differentiated male and female gonadalareas. The gonadal index varies throughout the yearwith maximum values occurring in January, March andJuly, and minimum ones in August and September. Partial spawning (with respect to the individual andthe population) occurred from January to February andMarch to May. The major spawning event coincided withthe end of the period during which bottom watertemperature increased to temperatures above 26°C(July–August). Subsequently temperature decreased to22°C, with a period of gonadal restoration andincreasing gonadal index. Histological analysis ofthe gonads correlated with the gonadal index. 相似文献
960.